The invention relates generally to the field of supercapacitive desalination, and more particularly to supercapacitor desalination devices having high current efficiency, and methods of making the same.
Generally, supercapacitor desalination devices employ a pair of electrodes of reverse polarity. During a charging step, a feed stream is allowed to flow through the supercapacitor desalination device. The ionic species in the feed stream are adsorbed on the surface of the oppositely charged electrodes, thereby de-ionizing the feed stream to produce a dilute output. During a discharging step, the ionic species are desorbed from the surface of the electrodes and into the feed stream to produce a concentrate output.
Further, ions having the same charge as that of the electrodes (hereafter referred to as similarly charged ions) are present inside the pore volume of the porous material of the electrodes. During the charging step, once the voltage is applied some of these similarly charged ions may be expelled from the electrode and be added into the feed stream. This undesired migration of the pore volume ions consumes extra current and adds to the impurity of the feed stream. In such cases, purification of the feed stream can only occur when an excess of feed ions, over and above ions that are expelled from the pore volumes, are adsorbed by the electrodes. On the contrary, during the discharging step, besides desorption of the oppositely charged ions from the porous electrode to the feed stream, some of the similarly charged ions in the feed stream may also be adsorbed into the pore volume. Although, the adsorption of the similarly charged ions occurs at all concentrations but gets worse at higher concentrations.
Thus, there exists a need for a supercapacitor desalination device that has controlled migration of similarly charged ions.